The Phase II part of the study is an efficacy study of the association of the recommended dose of lenalidomide associated with GA101 in 2 separate populations of patients: relapsed/refractory aggressive lymphoma (diffuse large B-cell lymphoma and mantle cell lymphoma: cohort 1), relapsed/refractory follicular lymphoma (cohort 2) and previously untreated follicular lymphoma (cohorts 3 and 4). First, all patients will receive a combination of obinutuzumab and lenalidomide for a total of 6 cycles. Patients who achieve at least a partial response after 6 cycles will receive a maintenance treatment with obinutuzumab for 2 years and Lenalidomide for 1 year as tolerated, or until disease progression.